3 · Modal verbs
Must and need not: děi, bìxū and búyòng
obligation and its absence
Děi is the everyday “have to”, bìxū the firm “must” of rules — and the negative of both is búyòng.
得 — the character usually read de, here read děi — is spoken “have to, got to”: 我得走了, “I’ve got to go”. It is very common in conversation and rare in formal writing. Like every modal verb it goes before the main verb.
必须 is “must”: firmer, the word for rules, requirements and anything written down — 考试的时候必须关手机, “phones must be switched off during the exam”. Warm insistence is 一定要, “be sure to”: 你一定要来.
“Don’t have to” is 不用 in speech and 不必 in more formal language: 明天不用上班, “no work tomorrow”. There is no bù děi and no bù bìxū. English speakers build them anyway, because English makes “don’t have to” out of “have to”; Chinese uses a different word.
And “must not” is a third idea again: 不能 in speech, 禁止 on signs. “You don’t have to come” (你不用来) and “you mustn’t come” (你不能来) are as far apart in Chinese as they are in English.
The form
| have to (spoken) | 我得走了。 |
| must (a rule) | 你必须按时来。 |
| don’t have to | 你不用来。 |
| needn’t (formal) | 您不必担心。 |
| be sure to | 你一定要来。 |
| must not | 你不能来。 |
The rules one by one
The form this topic is about
得 is the spoken “have to”; it stands before the verb and is read děi.
太晚了，我得回家了。It’s late, I have to go home.
必须 is a firm “must”, the word for rules and requirements.
考试的时候必须关手机。Phones must be switched off during the exam.
“Don’t have to” is 不用 or 不必; neither 得 nor 必须 takes 不.
明天是星期天，你不用早起。Tomorrow is Sunday, so you don’t have to get up early.
“Must not” is a different idea: 不能, or 禁止 on signs.
你发烧了，不能去游泳。You’ve got a temperature — you mustn’t go swimming.
一定要 is a warm insistence: be sure to.
到了北京一定要给我打电话。Be sure to call me when you get to Beijing.
A closer look
One character, three readings
The character of 得 has two other jobs, each with its own reading. As de it links a verb to a description of how it is done: 他跑得很快, “he runs fast”. As dé it is “get, obtain”: 得到. Only before another verb, meaning “have to”, is it děi.
The position tells you which. After a verb it is de; in a word such as 得到 it is dé; as a modal verb, standing before the main verb, it is děi: 你得去, “you have to go”. The pinyin on this site always shows which one is meant.
Exceptions and special cases (1)
-
you meet 不得不
it means “have no choice but to” — a stronger must, not a negative.
雨太大了，我们不得不回家。The rain was so heavy that we had no choice but to go home.
It is two negatives: “cannot not”. Note the reading dé, not děi.
How to spot it
- 得
- 必须
- 不用
- 不必
- 一定要
Example sentences
我明天早上六点得起床。I’ve got to get up at six tomorrow morning.
这件事你得跟你妈妈商量一下。You’ll have to talk this over with your mother.
所有的乘客必须买票。All passengers must have a ticket.
你不用带钱，我请客。You don’t need to bring money; it’s my treat.
这张表必须用中文填。This form must be filled in in Chinese.
您不必客气。There is no need to stand on ceremony.
7 more example sentences
我的护照快过期了，得去办一个新的。My passport is about to expire; I need to get a new one.
你不用等我，先吃吧。You don’t need to wait for me — go ahead and eat.
参加比赛的人必须先报名。Anyone taking part in the competition must register first.
要下雨了，我们得快点儿走。It’s about to rain; we’d better hurry.
这点儿小事，你不必放在心上。It’s a small thing — there’s no need to take it to heart.
明天的会你一定要参加。You really must come to tomorrow’s meeting.
医生说我必须戒烟。The doctor says I must give up smoking.
Worth knowing (1)
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Búyòng xiè
不用谢, “no need to thank me”, is one of the everyday replies to thanks — the same “need not” as in this topic.
谢谢！——不用谢。Thanks! — No need to thank me.
The trap English speakers fall into
Watch out
English builds “don’t have to” out of “have to”, so learners put 不 in front of 得. That form does not exist in speech, and in writing the same two characters read bùdé mean “may not” — the opposite of what was meant. “Don’t have to” is its own word, 不用.
Have to is děi or bìxū; don’t have to is búyòng; mustn’t is bù néng.
Your turn
8 exercises on this topic. Your answers are checked in the browser; none of them leaves your device.